(1) Field of the Invention
This invention relates generally to camera modules and relates more specifically to focusing a digital camera module by a movable lens barrels using ball bearings.
(2) Description of the Prior Art
Digital camera modules are used with many electronic devices such as e.g. mobile phones, personal data assistants (PDAs), computers, etc. These camera modules have to be as small as possible, reliable, and easy to be used, robust and require minimal power consumption. Furthermore the design of the camera modules should allow low manufacturing cost, while the quality of the images has to conform to a high standard.
Therefore modern camera modules should allow auto-focusing and minimal friction of the bearing for a movable lens barrel in order to achieve precise focusing of the camera.
There are known patents dealing with the design of camera modules.
U.S. Patent Publication (US 2008/0037143 to Yoon) teaches a lens assembly has a driving actuator that includes a magnet, a yoke and a coil and is formed along a lens barrel that accommodates a lens unit for focusing and an auto-focus controlling apparatus comprises the lens assembly for camera module. The magnet or the coil has an internal diameter smaller than a maximal diameter of the lens barrel. Therefore, it is possible to manufacture much smaller lens assembly according to the present invention compared to the conventional ones and to reduce the possibility of component damages in the lens assembly in operating the camera module. A magnet, a yoke, and a coil are arranged adjacently to or along the outside of the lens barrel. Besides, leaf springs are formed respectively on the top of the lens barrel and the beneath the lens barrel. The leaf springs interconnect the lens barrel, which moves repeatedly up and down, with the magnet, yoke, and coil fixed to the lens barrel so that they function as supplying currents with both ends of the coil. The lens barrel and a driving actuator including the magnet, the yoke, and the coil for operating the lens barrel are accommodated in a housing through threaded couplings.
U.S. Patent Publication (US 2008/0225415 to Bogue et al.) discloses a camera module including an integral motor for rotating a lens unit of the camera module within a housing of the camera module. The housing includes a plurality of electromagnetic coils that function as a stator of the motor. The lens unit includes a plurality of ferrite elements and functions as a rotor of the motor. Rotation of the lens unit within the housing causes focal adjustment, such that the motor can be used as a component of an auto-focus system. A method for assembling the camera module is also disclosed. The individual coils are disposed adjacent the periphery of the lens barrel so that the plurality of electromagnetic coils surrounds the lens barrel of the lens unit. Control circuitry selectively energizes the electromagnetic coils to control the rotational movement of the rotor with respect to the stator.
U.S. patent (U.S. Pat. No. 4,400,071 to Tamura et al.) describes a mark finder for an auto-focus camera provided with a photographic field mark indicating a picture frame within the field of view of the finder, and a distance measuring area mark indicating the light metering field of a photo-electric in-focus detecting device, the above-described photographic field mark and the above-described distance measuring area mark are formed to be adjustable independently of each other. A spring is provided between the housing and a lock washer provided on the guide shaft at a suitable location, urging the lens barrel to move in the direction desired.